1. Field of the Invention
The present invention relates to a tightening tool such as an electric screwdriver used for screw-tightening operation.
2. Description of the Related Art
An example of a known electric screwdriver is disclosed in Japanese patent publication No. 3-5952, in which a clutch is used to connect a tool bit and a driving motor for transmitting the rotating torque. According to this technique, when the tightening tool or screw is tightened to a predetermined depth with respect to the workpiece, the clutch is promptly disengaged to stop transmission of the rotating torque according to the tightening depth.
According to the known screwdriver, the clutch is engaged when the user applies a pressing force on the body of the screwdriver, so that the torque of the driving motor is transmitted to the tool bit. In this respect, when the clutch comes into engagement, driving-side clutch teeth rotated by the driving motor contacts with the driven-side clutch teeth that is not yet rotated. As a result, noise may possibly be caused between the driving-side clutch teeth and the driven-side clutch teeth. In this respect, further improvement is required.